Overview
Calcium Hardness (CH) is another important parameter to follow when managing a hot tub. It contributes to having balanced water that is neither corrosive nor scale forming.
Why does this matter?
It’s important to distinguish the importance of calcium hardness based on the type of hot tub you own. For modern acrylic or fiberglass hot tubs, having a low calcium hardness won’t usually damage anything. An exception would be if you’re dealing with concrete or plaster spas, or a spa with internals that are not resistant to corrosion (rare for a modern manufactured spa).
Beyond concern for a low CH to leach minerals from the spa, there’s really two other reasons you should care about CH:
- CH contributes to having balanced water. Balanced water in a spa prevents the formation of scale which can damage heaters and pumps. A high calcium hardness in your hot tub means you’ll need a lower Total Alkalinity and pH to have balanced water. A lower calcium hardness in your hot tub means you’ll need a higher Total Alkalinity and pH to have balanced water.
- CH levels determine the foam potential of the water. A low CH can encourage more foam because CH binds to oils and soaps and inhibits them from foaming.
How do I measure CH?
A drop test kit is usually the best method for testing CH. You shouldn’t need to test this parameter often once it’s in your target range. Test strips are generally too unreliable to make dosing decisions.
I generally test CH weekly when I do a full panel test after topping off the water due to splash out, evaporation or carry out from swim suits.
What is a good CH for my hot tub?
In a modern manufactured spa, a CH of around 150 is recommended to prevent foam. In a plaster or concrete hot tub, you should pay more attention to a positive CSI (Calcium Saturation Index) for potential of corrosion.
How do I change CH in my hot tub?
You can increase CH by using a calcium hardness increaser product.
There’s currently no good way to remove calcium with chemicals. You either need to drain water and replace it with softer water, or use something like the Vanishing Act pillow from Hot Sprints to run your water through it to soak up the calcium.